My main objection isn't really which stone is which, it's that a simple explanation involving the backstone falling and lying where it fell (in the chamber) is being dismissed, but replaced with a very complex series of events involving several stones being moved, all in a short period of time between reported visits, but not being mentioned by anyone.

People like W.C. Borlase asked the locals about the sites he visited, surely someone would have mentioned a big engineering job being undertaken in recent times (living memory), wouldn't they?